Under certain circumstances it may be desirable or necessary to make a separation between two thin sheets of slack flexible material, such as paper or plastic. Since this sheet material has a low resisting moment to bending, such sheets are hard to separate, which certainly is a handicap when processing same in machines.
These sheets can constitute together a bag or may be used for the forming of a bag, and the separation of the sheets is necessary when the bag has to be provided with a valve for filling purposes. The filling can be done by means of a temporarily inserted mouth-piece (in the case of paper bags) or by means of a permanently inserted connecting valve (in case of plastics bags).
To open the bags, that means is to separate the superposed sheets, so that the mouth-piece or connecting valve can be inserted, an attempt is made to drive a pointed object between the sheets. Rather, than opening the bag, however, the two sheets are bent over, both in the same direction and the bag remains closed.
Still more difficult is getting access between a pair of slack sheets when these sheets have a very smooth surface. This is the case with some sorts of paper and virtually with all plastics materials. With such materials there exists a strong adhesion force (vacuumlike adhering). In the case of plastics materials there is still another factor to be added, viz. the fact that handling and processing of the material may provoke high electro-static charges causing the sheets to attract each other.
Accordingly this separation process does not lend itself to mechanisation and constitutes further, due to the labour-intensive character of this operation, the "bottle-neck" in the production.